Glossary 9 Foreword 10 1 Design considerations 11 1.1 Introduction 11 1.2 Client's general requirements 11 1.3 The ground 11 1.3.1 The concept of effective stress 11 1.3.2 Ground profile 13 1.3.3 Groundwater conditions 14 1.3.4 Global movements 14 1.4 Methods and types of construction 15 1.5 Retaining walls 16 1.6 Foundations 17 1.7 Ground gases 17 1.8 Site Investigation 17 1.9 Structural analysis 18 1.10 Protective measures 18 1.11 Durability and waterproofing 18 1.12 Safety 19 1.13 Legal and contractual issues 19 1.14 Communications 19 2 Ground movement 21 2.1 Introduction 21 2.2 Causes of movement when excavating 21 2.2.1 General 21 2.2.2 Clays 21 2.2.3 Granular soils 23 2.2.4 Mixed alluvial soils (sands/silts/clays) 24 2.2.5 Soft rocks 25 2.2.6 Fill materials 25 2.3 Quantifying movements due to basement construction 25 2.3.1 General 25 2.3.2 Vertical movement within the basement area 25 2.3.3 External movements 26 2.3.4 Effect of excavation geometry 29 2.4 Effect of ground movement on surrounding structures and services 29 2.4.1 General 29 2.4.2 Tolerance of buildings 30 2.5 Concluding remarks on predicting ground movement 30 2.6 Monitoring ground movements 32 3
3 Groundwater control 36 3.1 Introduction 36 3.2 Methods of groundwater control 37 3.2.1 Pumping from sumps 37 3.2.2 Wellpointing 37 3.2.3 Disposal of pumped water 38 3.2.4 Pumping from deep wells 38 3.2.5 Pumping using cut-offs 38 3.2.6 Relief wells 39 3.2.7 Recharging 39 3.2.8 Grouting 40 3.2.9 Ground freezing 40 3.3 Permanent groundwater control 40 3.4 Changes in groundwater regime 41 4 Methods and type of construction 44 4.1 Introduction 44 4.2 Methods of construction 44 4.2.1 Construction in open excavation 44 4.2.2 Construction within soil slopes of increased inclination 44 4.2.3 Bottom-up excavation 44 4.2.4 Top-down construction 45 4.2.5 Semi-top-down construction 47 4.2.6 Bottom-up and top-down methods 47 4.2.7 Flying shores 48 4.2.8 Observational Method 48 4.3 Types of wall 49 4.3.1 Sheet piles 49 4.3.2 King post walls 51 4.3.3 Contiguous bored pile walls 51 4.3.4 Secant pile walls 52 4.3.5 Diaphragm walls 52 4.4 Selection of wall type 53 4.5 Types of support system 53 4.5.1 Temporary restraint 54 4.5.2 Permanent restraint 56 4.5.3 Effect of installation of sheet piles and soil retention walls 56 4.5.4 Groundwater 56 5 Design and analysis of retaining walls 59 5.1 Introduction 59 5.2 Stability considerations 59 5.2.1 Limiting earth pressures 59 5.2.2 Water pressures and the effects of seepage 59 5.2.3 Gravity walls 59 5.2.4 Cantilever walls 60 5.2.5 Singly-propped walls 60 5.2.6 Multi-propped walls 60 5.2.7 Circular basements 61 5.2.8 Factors of safety 62 5.2.9 Temporary works design 62 5.2.10 Base heave failure 63 4
5.3 Earth pressures 64 5.3.1 Backfilled walls 64 5.3.2 Initial in-situ earth pressures and the coefficient of earth pressure at rest K o 64 5.3.3 Effects of wall and prop stiffness 65 5.3.4 Design earth pressures 65 5.4 Design of wall members 65 5.4.1 Applied wall forces 66 5.4.2 Bending moments and shear forces 66 5.4.3 Wall movements and cracking 66 5.5 Computer programs for designing retaining walls 66 5.5.1 Limit equilibrium programs 66 5.5.2 Beam-on-spring model 67 5.5.3 Boundary element programs 67 5.5.4 Full numerical analysis 67 6 Foundations 69 6.1 Introduction 69 6.2 Loads 69 6.3 Water pressures 69 6.3.1 Buoyancy and flooding 70 6.3.2 Water pressure on foundations 70 6.4 The influence of excavation on strength and bearing capacity 70 6.5 Ground movements 72 6.6 Spread foundations 72 6.7 Bearing capacity of piles 73 6.8 Piled rafts and piles in tension 73 6.9 The use of piles to strengthen soils in front of a retaining wall 74 6.10 Vertical bearing capacity of piled walls 74 7 Gas in deep basements 77 7.1 Introduction 77 7.2 Precautions 78 8 Site Investigation 79 8.1 Introduction 79 8.2 Desk Study 79 8.3 Physical investigation of the site 80 8.4 Groundwater investigation 80 8.5 Parameters for design 80 8.5.1 Classification tests 80 8.5.3 Stiffness parameters 8.5.4 In-situ stresses 82 8.6 Chemical testing 82 9 Excavation 85 9.1 Introduction 85 9.2 Methods of excavation 85 9.3 Considerations affecting the use of plant in deep excavations 85 9.4 Unrestricted sites 85 5
9.5 Restricted sites 85 9.5.1 General 85 9.5.2 Diaphragm walls 86 9.6 Obstructions 9.7 General removal of spoil from site 86 9.8 Piling within basements 86 10 Protective measures 87 10.1 Introduction 87 10.2 Internal structural measure: strutting and sequence 87 10.3 External structural measure: underpinning 88 10.3.1 General advice 88 10.3.2 Shallow underpinning 89 10.3.3 Deep underpinning 91 10.4 External structural measure 91 10.4.1 Strengthening 91 10.4.2 De-sensitisation 92 10.4.3 Load transfer 92 10.5 Ground treatment 92 10.5.1 Compensation grouting 92 10.5.2 Ground improvement 93 10.5.3 Structural strengthening 94 10.5.4 Groundwater control 94 11 Materials, workmanship, durability and water-resisting construction 95 11.1 Introduction 95 11.2 Reinforced concrete design for foundation engineering structures 95 11.3 Durability 96 11.4 'Waterproofing' 97 11.5 Structural details 100 11.5.1 Crack control 100 11.5.2 Thermal effects 101 11.5.3 Flexural cracking 101 11.6 Design guidelines 102 11.7 Maintenance 102 11.8 Basement grades, types and details 102 11.9 Steel construction 102 11.9.1 Materials and sections 102 11.9.2 Durability 103 11.9.3 Water-resisting construction in steel sheet-piled structures 11.23 103 12 Safety considerations 109 12.1 General 109 12.2 Legal 109 12.2.1 Health and Safety at Work, etc. Act 1974 109 12.2.2 Management of Health and Safety at Work Regulations 1999 109 12.2.3 Construction (Design and Management) Regulations 1994 109 12.2.4 Construction (Health, Safety and Welfare) Regulations 1996 110 12.2.5 Confined Spaces Regulations 1997 110 6
12.3 Hazards 110 12.3.1 Underground and overhead services 110 12.3.2 Excavation stability 110 12.3.3 Exceptional circumstances 110 12.3.4 Backfill materials 110 12.3.5 Diaphragm walls 110 12.3.6 Strutting and shoring 110 12.3.7 Ramps and site transport 111 12.3.8 Settlement 111 12.3.9 Piling 111 12.3.10 Erection and support of steel reinforcement 111 12.3.11 Methane, oxygen deficiency and other atmospheric hazards 111 12.3.12 Fencing, lighting, etc. 111 12.4 Electricity 111 12.5 Noise and vibration 112 12.6 Contaminated ground 112 12.7 Failures leading to injury or death 112 12.8 Supervision of work on site 112 12.9 Practical difficulties in construction on site 112 12.10 Risk assessment 113 12.10.1 Production of a typical risk assessment 114 13 Legal and contractual issues 119 13.1 Forms of contract and procedures 119 13.2 Problems specific to basement contracts 120 13.3 Specialist contractors 120 13.4 Responsibility for Site Investigation 120 13.5 Delineation of temporary and permanent works 121 13.6 Responsibility for temporary works 121 13.7 Use of permanent works to support temporary works 122 13.8 Adjacent structures 122 13.9 Statutory requirements 123 14 Communications 124 14.1 Importance of communications 124 14.2 Information supplied by the engineer 124 14.3 Information submitted by the contractor 124 14.4 Post-contract and construction stages 127 14.5 Quality requirements 127 Appendix A Archaeological implications 128 Appendix B Special services: requirements for deep basements 130 B.1 Introduction 130 B.2 Requirements for fire-fighting ventilation and smoke outlets 130 B.3 Plant rooms 130 Appendix C Statutory requirements (see also Chapter 12) 131 7
Appendix D Monitoring 133 D.1 Introduction 133 D.2 Precise level 133 D.3 Total station 134 D.4 Inclinometers 134 D.5 Electrolevels 134 D.6 General 135 Appendix E The Observational Method (OM) 136 E.1 Introduction 136 E.2 The traditional predefined design method and the Observational Method 136 E.3 Recent developments in using the Observational Method 138 E.4 Implementation 138 E.5 Progressive modification approach 138 E.6 Risk, contractual aspects and value engineering 139 Index 141 8